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Description
After landing on the skin of a mammalian host, female mosquitoes start probing this tissue for a blood vessel, salivating and moving the mouthparts in a stereotypical way. Intradermal probing must be fast and efficient, being a necessary but hazardous step in mosquitoes' life cycle, as they need to acquire and digest blood to complete egg development.
We have recently characterised the role of Labrum Interacting Protein of the Saliva (LIPS)-2 in modulating intradermal probing in the tiger mosquito Aedes albopictus. LIPS-2 is expressed in female mosquito salivary glands and secreted in the host skin at the bite site. The LIPS-2 gene is restricted to the Culicinae subfamily, including Aedes and Culex mosquitoes, while is absent in the Anophelinae subfamily. We observed that knocking down the expression of LIPS-2 protein in Ae. albopictus female mosquitoes increased their probing time while feeding on a human volunteer. Here, we combine genetic engineering, electron microscopy imaging, and behavioural assays to gain mechanistic insight into this phenotype.
LIPS-2 binds to the tip of the labrum, the elongated and sharp-pointed stylet forming the food channel within the mosquito mouthparts. LIPS-2 binding leads to a modification of the height of labral ridges, two cuticular structures located at the tip of the labrum. These structures can be observed in Ae. albopictus, Aedes aegypti, and Culex pipiens mosquitoes, but are absent in Anopheles stephensi, as assessed by scanning electron microscopy. Labral ridges were previously described to each host one pair of sensory dendrites called labral ridges receptors (lrr). Despite being suggested to have a proprioceptive role, the function of these structures in mosquito sensation during feeding remains to be understood.
To gain mechanistic understanding in the functioning of LIPS-2 in modulating probing dynamics, we characterized a LIPS-2 knockout line using the BiteOscope, a platform allowing the quantification of landing, probing, and engorging of mosquitoes on modifiable synthetic substrates. Additionally, electropenetrography was implemented to observe, record, and quantify probing and engorging behaviours in the LIPS-2 knockout line. Together, these experiments represent a base for a deeper understanding of the function of LIPS-2 in the modulation of intradermal probing in Aedes mosquitoes.
